Isolated high purity X-chromosome bearing or Y-chromosome bearing populations of spermatozoa can be utilized to accomplish in vitro or in vivo artificial insemination of or fertilization of ova or oocytes of numerous mammals such as bovids, equids, ovids, goats, swine, dogs, cats, camels, elephants, oxen, buffalo, or the like. See also, U.S. Pat. No. 5,135,759, hereby incorporated by reference.
However, conventional technologies for separating spermatozoa into X-chromosome bearing and Y-chromosome bearing populations can result in spermatozoa populations having low purity. Regardless of the separation method spermatozoa have not been routinely separated into X-chromosome bearing and to Y-chromosome bearing sperm samples having high purity, such as 90%, 95%, or greater than 95%.
A number of techniques, directly or indirectly based on differences in size, mass, or density have been disclosed with respect to separating X-chromosome bearing from Y-chromosome bearing spermatozoa As disclosed by U.S. Pat. No. 4,474,875, a buoyant force is applied to all sperm cells simultaneously and X-chromosome bearing and Y-chromosome bearing spermatozoa may then be isolated at different locations in the separation medium. U.S. Pat. No. 5,514,537 discloses a technique whereby spermatozoa traverse a column packed with two sizes of beads. The larger X-chromosome bearing spermatozoa become isolated in the layer containing the larger beads, while the smaller Y-chromosome bearing spermatozoa become isolated in the layer containing the smaller beads. U.S. Pat. No. 4,605,558 discloses that spermatozoa may be made differentially responsive to a density gradient and U.S. Pat. No. 4,009,260 exploits the differences in migration-rate, or swimming-speed, between the Y-bearing spermatozoa, and the X-chromosome bearing spermatozoa, through a column of retarding medium.
A problem common to each of the above-mentioned technologies may be that they each act on all the spermatozoa in a ‘bulk-manner’, meaning that all the spermatozoa undergo the same treatment at the same time, and the Y-chromosome bearing sperm cells come out faster, earlier, or at a different position than X-chromosome bearing sperm cells. As such, individual sperm cells may not be assessed and there may be no actual ‘measurement’ of volume, mass, density, or other sperm cell characteristics. One-by-one assessment of sperm cells can provide advantages in that the actual separation process can be monitored, and objective quantitative data can be generated even during the separation process, and separation parameters altered as desired. Furthermore, these technologies may not be coupled with flow cell sorting devices.
Flow cytometer techniques for the separation of spermatozoa have also been disclosed. Using these techniques spermatozoa may be stained with a fluorochrome and made to flow in a narrow stream or band passing by an excitation or irradiation source such as a laser beam. As stained particles or cells pass through the excitation or irradiation source, the fluorochrome emits fluorescent light. The fluorescent light may be collected by an optical lens assembly, focused on a detector, such as a photomultiplier tube which generates and multiplies an electronic signal, which may then be analyzed by an analyzer. The data can then be displayed as multiple or single parameter chromatograms or histograms. The number of cells and fluorescence per cell may be used as coordinates. See U.S. Pat. No. 5,135,759, hereby incorporated by reference. However, with respect to this type of technology a variety of problems remain unresolved and isolating highly purified populations of X-chromosome bearing or Y-chromosome bearing sperm cells be difficult.
A significant problem with conventional flow cytometer technologies can be the orientation of objects, particles, or cells in the sheath fluid stream. This can be particularly problematic when the object or cell is irregular in shape with respect to more than one axis, such spermatozoa for example. One aspect of this problem may be establishing the initial orientation of the object within the sheath fluid stream. A second aspect of this problem may be maintaining the orientation of the object with respect to the detector (photomultiplier tube or otherwise) during the period that emitted light from the object is measured.
Another significant problem with conventional flow cytometer technologies can be the failure to encapsulate the objects or cells in a droplet of liquid. Especially, when droplets are formed around irregularly shaped objects the droplet may not be of sufficient size to completely surround all the features of the objects or cells. For example, during flow cytometry operation as above-described droplets can be formed at very high speed, even as many as 10,000 to 90,000 droplets per second and in some applications as many as 80,000 droplets per second. When spermatozoa are encapsulated into droplets, especially at these high rates of speed, a portion of the tail or neck may not be encapsulated in the droplet. That portion of the tail or neck not encapsulated in the droplet may then be responsive with the nozzle or may be responsive to the environment surrounding the droplet in a manner that interferes with subsequent droplet formation or with proper deflection of the droplet. As a result some of the spermatozoa may not be analyzed at all reducing the efficiency of the procedure, or may not be resolved sufficiently to be assigned to a population, or may be deflected in errant trajectories, or a combination of all may occur.
Another significant problem with conventional flow cytometer technologies, as well as other technologies, can be a coincidence of measurable events. One aspect of this problem can be that the incident light flux from a first event continues to produce signals after the incident light flux from a second event starts to generate a signal. As such, the two events remain at least partially unresolved from one another. Another aspect of this problem can be that two or more events are simultaneously initiated and the incident light flux comprises the contribution of all the events. As such, the multiplicity of events may not be resolved at all and the objects corresponding to the multiplicity of events can be incorrectly assigned to a population or not assigned to a population at all, or both. Specifically, with respect to flow cytometry, individual particles, objects, cells, or spermatozoa in suspension flow through a beam of light with which they interact providing a measurable response, such as fluorescent emission. In conventional flow cytometry, Hoechst stained spermatozoa traverse a laser beam resulting in a fluorescent light emission. The fluorescent light emission from the excited fluorochrome bound to the DNA can be bright enough to produce an electron flow in conventional photomultiplier tubes for a period of time after the actual emission event has ended. Moreover, in a conventional flow cytometer, the laser beam can produce a pattern having a height of 30 μm while the width can be approximately 80 μm. The nucleus of a bovine spermatozoa which contains fluorochrome bound DNA can be about 9 μm in length making the height of the laser beam some three (3) times greater than the nucleus. This difference can allow for the laser excitation of the bound fluorochrome in more than one spermatozoa within the laser beam pattern at one time. Each of these conventional flow cytometry problems decreases the ability to resolve individual events from one another.
Another significant problem with conventional flow cytometer technologies, and other technologies, can be that irregularly shaped objects, such as spermatozoa, generate differing signals (shape, duration, or amount) depending on their orientation within the excitation/detection path. As such, individuals within a homogenous population can generate a broad spectrum of emission characteristics that may overlap with the emission characteristics of individuals from another homogenous population obviating or reducing the ability to resolve the individuals of the two populations.
Another significant problem with conventional flow cytometer technologies, and other technologies, can be that objects are not uniformly exposed to the excitation source. Conventional beam shaping optics may not provide uniform exposure to laser light when the objects are close to the periphery of the beam.
Another significant problem with conventional flow cytometer technologies can be that objects, such as spermatozoa, can be exposed to the excitation source for unnecessarily long periods of time. Irradiation of cells, such as spermatozoa, with laser light may result in damage to the cells or to the DNA contained within them.
Another significant problem with conventional flow cytometer technologies can be that there may be a disruption of the laminar flow within the nozzle by the injection tube. Disruption of the laminar flow can change the orientation of irregularly shaped objects within the flow and lower the speed of sorting and the purity of the sorted populations of X-chromosome bearing sperm or Y-chromosome bearing spermatozoa.
There may be additional problems with technologies that utilize stain bound to the nuclear DNA of sperm cells. First, because the DNA in the nucleus is highly condensed and flat in shape, stoichiometric staining of the DNA may be difficult or impossible. Second, stained nuclei may have a high index of refraction. Third, stain bound to the DNA to form a DNA-stain complex may reduce fertilization rates or the viability of the subsequent embryos. Fourth, the DNA-stain complex is typically irradiated with ultra-violet light to cause the stain to fluoresce. This irradiation may affect the viability of the spermatozoa. Due to these various problems, it may be preferable to use a method that requires less or no stain, or less or no ultra-violet radiation, or less or none of both.
With respect to generating high purity samples of X-chromosome bearing sperm cell or Y-chromosome bearing sperm cell populations (whether live, fixed, viable, non-viable, intact, tailless, or as nuclei), or generally, with respect to detecting small differences in photogenerated signal between serial events having relatively high incident light flux, or with respect to orienting irregularly shaped objects in a fluid stream, or eliminating coincident events within an optical path, or removing undesirably oriented objects from analysis, the instant invention addresses every one of the above-mentioned problems in a practical fashion.